Cathode-ray deflecting means



Aug. 21; 1945. I s. HANSEN 2,383,308

' I CATHODE-RAY DEFLECTING MEANS Fild May 8, 1941 2 Sheets-Sheet l .Figl.

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Aug. 21, 1945. s. HANSEN CATHODE-RAY DEFLECTING MEANS v Filed May 8, 1941 2 Sheets-Sheet 2 .IhVentOT": i Siegfried Hahse Cb His t ad, torney.

Patented Aug. 21, 1945 CATHODE-RAY DEFLECTING MEANS,

Siegfried Hansen, Schenectady, N. .Y., assig'nor to General Electric Company, a corporation of New York Application May 8, 1941, Serial No. 392,503 '4 Claims. (01. 250-151) The present invention relates to cathode-ray deflecting means adapted for use with television image-reproducing tubes and the like.

For many uses of cath'ode-raytubes (including tube wall. This may be done either by electrostatic or magnetic deflecting means, magnetic deflection beingmore widely used in current television practice.

Various magnetic structures have been proposed for producing the desired deflection, but the structures heretofore availablefare open to the objection of undue complexity, such com-4 plexity being mainly a consequence of difficulties encountered in producing uniform deflecting action over the entire fleld of deflection of the cathode-ray. In order to provide a simplified'arrangement it has been suggested to employ a rectangular deflecting frame or yoke having similar coils on all four legs, parallel coils being so connected that their leakage'flel'ds are in a common direction. However, due to the space require ments of the various coils, it is not possible to have the coils extend for theentire length of the legs which they respectively surround, and certain of the advantages which might be expected to result from this type of construction are, therefore, not realizable. In particular, the inability of the various coils to extend into the corners of the magnetic frame produces suflicient distortion of the field produced within the frame to cause non-uniform deflection and defocusing of the cathode-ray at some points of its travel.

It is an object of the present invention to provide an improved form of rectangular deflecting yoke which while free of the operational difilculties noted in the foregoing, isnevertheless characterized by a high degree of compactness and by low manufacturing cost.

The features which I desire to protect herein are pointed out in the appended claims. The inventionitself maybest be understood by reference to the following description taken in connection with the drawings in which Fig. 1 is a perspective view of a cathode-ray tube apparatus including. a magnetic ray-deflecting system embodying the present invention; Fig. 2 is a sectional view illustrating in detail the ray-deflecting system of Fig. 1; Figs. 3 to-5 inclusive are diagrammatic representations useful in explaining the invention; and Figs. 6an'd 7 are views which illustrate certain details of my improved deflecting yoke. at an intermediate stage of manufacture.

Referring particularly to Fig. 1, there is shown a cathode-ray tube of which the enclosing glass envelope comprises a bulbous portion in and an elongated neck portion ll, these portions being joined in end-lto-end relation. Within the en'- velope and at the extremity of the shaft portion ii there i provided an'electron gun I3 including a cathode and suitable control and focusing electrodes (not shown in detail). The electron stream or cathode ray projected from the gun i3 is accelerated longitudinally of the envelope by means of a high voltage anode consisting, for example, of a conductive coating applied to the interior wall surface of the envelope as indicated at l5. After traversing the envelope the ray impinges on the envelope end wall H, which in the case illustrated provides an extended and generally planar surface. The wall I! may be provided internally with an electron-responsive coating adapted to fluoresce at theregion of impingement of the-electron stream.

In theuse of the tube as a television picturereproducing agency, for example, it is necessary to provide means for deflecting the electron stream both horizontally and vertically to cause it to scan a selectedarea of the envelope wall (say the area indicated by the dotted line I8). In the present case the means provided for this purpose comprises an improved form of magnetic yoke adapted to be positioned about the axis of the cathode-ray tube as indicated at 20 in Fig. 1, Fig. 1 shows only the external aspects of the casing in which the sweep yoke is enclosed, the details of the yoke-being illustrated more fully in Fig. 2.

According to the present invention the yoke or deflecting system comprises a rectangular (preferably square) ferromagnetic frame 2i having a central opening of sufficient size readily to accommodate the neck of the cathode-ray tube. In the arrangement illustrated the upper and lower legs of the frame are respectively surrounded by layer wound coils 22 and 23 which are of uniform thickness throughout and which established by the various coils is as indicated by the letters N and S applied to the coils, it being understood, of course, that the polarities shown apply only at a particular instant during the defiecting cycle.

As a result of the fact that the coils extend over the full length of the frame legs the magnetomotive force gradient within the frame is uniform at all points along the coils and throughout the deflecting space. It will be readily seen, however, that this very fact (extension of the coils 22 and 23 across the entire frame) necessarily precludes a similar arrangement of coils on the remaining legs of the frame. Obviously any coils applied to the other legs must be foreshortened by an amount corresponding to the thicknes of the coils 22 and 23.

The practical efiect of this latter consideration is illustrated by the diagrammatic representations of Fig. 3 and Fig. 4, the former figure corresponding to th case of coils extending along the entire length of the frame legs and the latter illustrating the conditions existing in connection with coils which are shortened because of space requirements or other reasons. In both figures, 26 represents a magnetic core and 21 and 28 are coils assumed to be connected so that their leakag fields are in a common direction, the reference numerals being primed in connection with Fig. 4 for purposes of diiferentiation.

In Fig. 3, it will be observed that the equipotential lines of magnetic force (designated by the dash lines A) are substantially straight throughout the deflecting region. In Fig. 4, on the other hand, the corresponding lines A show considerable curvature at all points materially spaced from the axis of symmetry. While this distortion may not be great enough in any given case materially to afiect the shape of the scanned area (the raster) it is found to produce serious defocusing of the electron beam when the beam approaches the boundaries of the deflecting re gion. Defocusing produced in this way manifests itself in loss of definition at the edges of the picture image.

The present invention overcomes the difliculties noted in the foregoing by combining full-length coils such as the coils 22 and 23 with shortened coils applied to the remaining two legs of the defiecting yoke and having auxiliary means for minimizing the field-distortion thereby incurred. The arrangement shown in Fig. 2 comprises spool-wound coil sections 29 and 30 which cover the central portions of the vertical legs of the fram 2| and which are of uniform thickness throughout. These coil sections 29 are provided with supplementaary end sections 29' and 30' respectively which are of greater thickness than the main sections and which extend far enough to abut against the lateral surfaces of the coils 22 and 23, thus using all the available space. The end coil sections are connected in series with the respective central sections and comprise in effect continuous extensions of them. In use, all the coil sections are energized in such a manner (e. 2., by series connection) that their leakage fields are in a common direction. The end sections 29' and 39'. while shown as separate entities. may obviously just as well be formed by correspondingly extending the main section 29 and 30 and by winding on extra end turns. Accordingly. where the term additional end turns is used herein and in the appended claims it should be understood that it is intended to include an arrangement such as that of Fig. 2 in which the turns in question are physically separated from the principal coil structure.

The thickness of the end sections 29' and 30' is determined by the consideration that the total number of turns on the vertical legs of the frame should be the same as would be the case if the main coil parts were extended to cover the entire length of these legs. In a particular instance, it has been found advantageous to make the end sections twice the thickness of the central sections 29-30, in which case the axial extent of these end sections is made equal to the thickness of (one of) the coils 22 and 23 plus twice the thickness of (one of) the radially extending flanges of the winding forms 32-33.

The beneficial results obtained by th use of a coil construction of the type described above are illustrated in Fig. 5, which shows a magnetic netic lines obtained with this arrangement are parallel over a substantial portion of the region within the frame so that defocusing of the beam within this region is avoided.

In order to meet the public preference for a relatively elongated image it is customary in connection with the operation of television picture tubes to cause the scanned area to be of greater breadth than height. In connection with a deflection yoke of the character described herein this result may be obtained most effectively by positioning the yoke so that the coil 22 and 23 are parallel to the top and bottom bounda ies of the scanned area, this arrangement requiring that these coils be excited with the vertical sweep potential. The horizontal sweep potential must obviously be applied to the coils 29 and 30. By superimposing the representations of Figs. 3 and 5 it will be observed that mode of operation specified will provide a rectangular region of distortion-free deflection having its greatest dimension in the horizontal direction, a condition which obviously coincides with the desired shape of the picture-image as called for above.

A principal advantage of the deflecting yoke onstruction described in the foregoing consists in the inherent simplicity of the yoke and i s resultant ease of manufacture. In fabricating the yoke. it may be initially formed in two parts each constituted of L-shaped laminations stacked in such a wav as to leave unfilled gaps between the extremities of alternate laminations as indicated at M in Fi 6. After the laminations are stacked to the desired de th the reformed coils ma he. slipped over the top of the stack to produce a structure such as is, illustrated in Fig. '7. When two such structures have been prepared they are assembl d into a sin le rectangular ,voke by dovetailing the laminations oi the two laminar stacks into interlocking enga ement at their extremities. Finally. the various coils are connected in series in such a sense as to assure the desired cooperation of their lea age fields. the coil 22 bein connected in series with the coil 23 and the coils 29. 29', 30 and 30' being also serially connected with one another. Each set of serially connected co ls is then provided with a pair of externally accessible terminals, and the whole deflecting yoke is enclosed in a metallic container 20 (see Figs. 1 and 2) having circular openings (such as the opening 42 of Fig. 2) a ropriately positioned to receive the neck of a cathode-ray tube. The container, if made of a highly conductive metal such as copper, acts as an eddy-current shield to minimize the inductance of the various coils due to their external leakage fields. deflecting system may then be assembled with a cathode-ray tube in the manner indicated in Fig. l, the coils 22 and 23 being positioned to provide vertical sweep action and the coils 29 and 30 being arranged to provide horizontal sweep action.

While the invention has been described mainly by reference to a television receiving tube, it will be understood that it is equally capable of application in connection with other types of cathoderay devices such as television camera tubes and the like.

I aim in the appended claims to cover all such equivalent variations of structure and use as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a cathode-ray tube and a ray-deflecting system, said system comprising a rectangular ferromagnetic frame surrounding the axis of the said tube, a first pair of coils respectively surrounding parallel legs of said frame and extending substantially the entire length of such legs, said coils being of uniform cross section throughout and being connected so that their leakage fields within the space enclosed by the frame are in a common direction transverse to the axis of the tube, a second pair of coils respectively surrounding the remaining two legs of the frame and also connected so that their leakage fields within the space enclosed by the frame are in a common direction, the members of said second pair of coils having their extremities substantially abutting against the surfaces of the first coils and having additional end turns to improve the uniformity of the deflecting field established by them, and terminals associated with the various coils 'for' connecting the respective coil pairs to separate sources of deflecting potential.

The completely enclosed 2. In combination, a cathode-ray tube having an extended end wall positioned in the path of the cathode-ray and deflecting system for causing the ray to scan the said wall over a rectangular area of greater length than height; the deflecting system comprising a substantially square ferromagnetic frame surrounding the axis of the 4 tube and having its legs respectively parallel to sides of the said scanned area of the tube wall, a pair of coils respectively surrounding the legs of the frame which parallel the long dimension of the scanned area and extending for substantially the entire length of said legs, said coils being of uniform thickness throughout and being connected so that their leakage fields with the space encompassed by the frame are in a common direction, a second pair of coils respectively surrounding the remaining two legs of the frame and having their extremities in abutment with the lateral surfaces of the first-named coils, said secondnamed coils being also connected so that their leakage fields are in a common direction and having additional end-turns to improve the uniformity of the. field produced by them within the frame, and terminal connection for permitting the application of a vertical scanning signal to the first-named pair of coils and a horizontal scanning signal to the second-named coils.

3. A cathode-ray deflecting system comprising a rectangular ferromagnetic frame, a first pair of coils respectively surrounding parallel legs of said frame and extending for substantially the entire length of said legs, said coils being of substantially uniform thickness throughout and being connected so that their leakage fields within the space encompassed by the frame are in a common direction, and a second pair of coils respectively surrounding the remaining two legs of the frame and having their extremities in substantial abutment with the lateral surfaces of the firstnamed coils, said second-named coils also being connected so that their leakage fields are in a common direction, and being provided with additional end-turns, whereby the non-uniformity of the deflecting field of the second-named coils resulting from their failure to extend for the entire length of the frame leg which it surrounds is reduced.

4. A cathode-ray deflecting system comprising a rectangular ferromagnetic frame, a first pair of spool-wound coils respectively surrounding parallel legs of said frame and extending for substantially the entire length of said legs, the said coils being of substantially uniform thickness throughout and being connected so that their leakage fields are in a common direction, a second pair of spool-wound coils centrally surroundin the remaining two legs of the frame and extending for a major portion of the length of the legs, said second-named coils also being connected'so that their leakage fields extend in a common direction, and auxiliary spool-wound coils abutting the ends of the second-named coils and filling the spaces remaining between the extremities of such coils and the lateral surfaces of the first-named coils, said auxiliary coils being of greater thickness than the second-named coils and serving to improve the uniformity of the deflecting-field produced by such coils.

. SIEGF'RIED HANSEN. 

